1. Field of the Invention
The present invention relates to a method and an apparatus for smoothly unreeling an elongate photographic photosensitive film and cutting the elongate photographic photosensitive film to various pre determined lengths.
2. Description of the Related Art
For producing and packaging a photographic photosensitive film, it has been customary to perform various steps including the steps of producing a film of given length, winding the film, placing the wound film into a film cartridge, and inserting the film cartridge into a case.
These various steps are carried out by a facility, i.e., a film producing and packaging system, comprising a film supply unit for unwinding a film roll and cutting, i.e., trimming, the unwound film to a film of given length, i.e., a sized film, a film coiling unit for coiling the sized film on a spool thereby to produce a film coil, a cartridge producing unit for staking a cap on an end of a tubular cartridge blank sheet thereby to produce a cartridge with one open end, an assembling unit for inserting the film coil into the cartridge and staking another cap on the open end of the cartridge thereby to produce an assembled cartridge, and an encasing unit for placing the assembled cartridge into a case and attaching a case cap on an open end of the case thereby to produce a packaged film product.
For trimming an elongate photographic photosensitive film coil into a sized film and coiling the sized film on a spool, it is the usual practice to operate a feed mechanism such as a sprocket, for example, disposed upstream of a cutting mechanism, to deliver the elongate photographic photosensitive film through the cutting mechanism. After a leading end of the elongate photographic photosensitive film is inserted in a groove in the spool disposed in an inserting position in the film coiling unit, the elongate photographic photosensitive film is fed by a predetermined length between the inserting position and a cutting position in the cutting mechanism. Then, the elongate photographic photosensitive film is trimmed by the cutting mechanism into a sized film with its leading end inserted in the spool.
Various packaged film products that are commercially available contain various sized films of 12, 24, and 36 exposures. These sized films can automatically be coiled around respective spools according to the process described above.
There have been demands for packaged film products containing sized films of 10 or less exposures, e.g., 5 through 10 exposures, typically for use as premiums. However, since sized films of 10 or less exposures are considerably short, before the leading end of the elongate photographic photosensitive film is inserted in the groove in the spool, a region to be trimmed of the elongate photographic photosensitive film is placed in the cutting mechanism. The operation sequence of the existing film producing and packaging system for producing packaged film products containing sized films of 12 or more exposures is different from an operation sequence for producing packaged film products containing sized films of 10 or less exposures, and hence does not lend itself to the production of packaged film products containing sized films of 10 or less exposures.
One solution would be to change the timing of operation of an actuator of the cutting mechanism for cutting an elongate photographic photosensitive film to various different sized films including those of 10 or less exposures. However, it would need a considerably complex control process to switch between different operation modes of the actuator.
In the film supply unit, after a film roll is installed on a reel shaft, the reel shaft is rotated by a servomotor or the like to unwind the film roll at a rate depending on the line speed of the film producing and packaging system which has been set for the type of the packaged film product to be manufactured. The film supply unit includes a perforator for perforating, at spaced intervals, one or both sides of the elongate photographic photosensitive film as it is unreeled from the film roll. The perforator has a sprocket whose teeth engage in the perforations and which is rotated to deliver the elongate photographic photosensitive film at the preset line speed of the film producing and packaging system.
Therefore, the reel shaft and the sprocket are rotated to feed the elongate photographic photosensitive film to a next process at the preset line speed of the film producing and packaging system.
However, if the film roll mounted on the reel shaft suffers diameter variations, then the peripheral speed of the film roll varies even when the reel shaft is rotated at a predetermined rotational speed. When the peripheral speed of the film roll varies, the elongate photographic photosensitive film unreeled from the film roll differs from the line speed of the film producing and packaging system. For example, when the diameter of the film roll becomes smaller, the peripheral speed of the film roll becomes smaller than the speed at which the elongate photographic photosensitive film is fed by the sprocket, resulting in greater tension applied to the elongate photographic photosensitive film.